The invention concerns a process for producing a sensor arrangement for measuring temperature, comprising a temperature-sensitive measuring resistance element which has a thin metal film as a resistance layer and contact surfaces on a ceramic substrate, wherein the resistance layer is covered by an electrically insulating protective layer, the contact surfaces, however, conduct electricity and are directly connected, mechanically fast, with conductor strips which are electrically insulated from one another on a high temperature-stable board, whereby the measuring resistance element at one end of the board is allocated contact surfaces for connection of a plug or cable.
For example, substrates or boards as carriers for passive or active structural elements are sufficiently known from German Patent DE 39 39 165 C 1 or German Utility Model DG 87 16 103 U1. Since most component parts find applications in temperatures ranging up to a maximum of 150.degree. C., the board material is usually designed only for this temperature range. As a rule, it is a matter of plastics which are often reinforced with inorganic materials. To the extent that a wireless bonding of the component parts is provided, as this is, for example, customary even for temperature measuring resistance elements for application as calorimetry sensors (German Patent DE 44 24 630 C1), this takes place through soft soldering and/or by means of conductive adhesives. These connection techniques on plastic boards are, however, completely unsuited for temperatures above 300.degree. C.
A sensor arrangement, likewise for calorimetry, is known from German Utility Model DE 295 04 105 U1, in connection with which a short (15 mm long) ceramic thin layer is used as the board. Since here use as a calorimetric sensor is indicated, one must proceed from the assumption that bonding by means of soft solder is provided. In order to guarantee a flawless bonding with a soft solder, this requires on the one hand a measuring resistance element with previously tin plated contact surfaces, and in addition several process steps: 1. Printing the board with a soldering paste; 2. "Reflow" burn-in of the soldering paste; 3. Placing the measuring resistance element on the soldering pads of the board for which an SMD adhesive is recommended for fixing the position; and 4. "Reflow" burning-in for connecting and melting the soldering pads. Aside from the fact that soft soldering is only suited for operating temperatures of 300.degree. C. at the highest, the procedure is characterized by many individual steps which make manufacture relatively expensive.
Further procedures for producing sensor arrangements with temperature measuring resistance elements for high temperature use according to the state of the art (documented for example in German Utility Models DGm 1 681 483, DGm 1 713 442, DGm 1 784 455, DGm 1 808 504, DGm 1 855 262, and German Patent 855 627) are so designed that, first of all, the connecting wires of the measuring resistance element are extended by electrically insulated connecting wires of the connecting cable. The connection of the quite thin connecting wires of the measuring resistance element to the usually thicker connecting wire of the lead is created by welding or hard soldering. If a fiberglass-coated lead is used, the insulation must first be stripped off. In order to rule out a short circuit during the operating state, however, some sort of an electrical insulation must be provided for the connecting wires of the measuring resistance element and for the region of the welding or hard soldering connection. Moreover, the connecting wires must be relieved of stress either by sealing material or by special ceramic shaped parts (see DGm 1 855 262). The electrical insulation of the connecting cable for high temperature use may be fulfilled by ceramic capillary tubes, which, however, entail a large proportion of the overall material costs and which, on account of their geometric dimensions, often stand in the way of a miniaturization. Alternatively, the insulation may be guaranteed by fiberglass jackets which are stiffened for production-related reasons by an organic impregnation. This impregnation must be removed in an extra annealing process. In addition, it is customary in fixing the position of the measuring resistance element to introduce a ceramic adhesive into the tip of the measuring insert protection tube. A high temperature measuring insert is therefore produced according to the state of the art with a multitude of individual components and process steps, which either cannot be automated, or can only be automated at great expense.